1. Field of the Invention
The present invention relates to self-bondable, electrically insulated, conductive substrates, and more particularly, the invention relates to bondable, electrically insulating heat curable coating compositions. More specifically, this invention is directed to an improved self-bondable magnet wire.
2. Description of the Prior Art
Adhesive varnishes and coatings have long been known in the art to be useful for providing self-bonding laminae and magnet wire. Self-bonding magnet wire, for example, can be wound into coils, which are then heated either externally or by internal resistance, to cause the bonding coating to fuse or thermally set to form rigid bonded coil structures. Laminates can be similarly formed. Among such self-bonding adhesive coating materials are certain polysulfones as disclosed in U.S. Pat. No. 3,676,814, issued July 11, 1972 to F. F. Trunzo et al. for HIGH TEMPERATURE ADHESIVE OVERCOAT FOR MAGNET WIRE; vinyls such as polyvinyl chloride or polyvinyl acetate as disclosed in U.S. Pat. No. 3,574,015, issued Apr. 6, 1971, to J. C. Blee for METHOD AND APPARATUS FOR JOINING CONDUCTORS; polyethylene, as disclosed in U.S. Pat. No. 3,974,016, issued Aug. 10, 1976 to V. E. Bondybey et al. for BONDING OF THERMOPLASTIC COATED CYLINDERS; polyvinyl acetals such as polyvinyl butyral as disclosed in U.S. Pat. No. 3,516,858, issued June 23, 1970, to A. F. Fitzhugh et al., for SELF-BONDING MAGNET WIRE AND PROCESS FOR PREPARING THE SAME; U.S. Pat. No. 3,300,843, issued Jan. 31, 1967, to T. Umewaka et al., for SELF-BONDING MAGNET WIRE AND METHOD; and U.S. Pat. No. 3,456,338, issued July 22, 1969, to D. W. Mohrman et al., for METHOD FOR CHANGING THE CONFIGURATION OF AND FOR BONDING ELECTRICAL COILS OF INDUCTIVE DEVICES; polyamide-imide enamel with residual solvent as disclosed in U.S. Pat. No. 4,346,136, issued Aug. 24, 1982, to J. H. Lupinski, for BONDABLE MAGNET WIRE COMPRISING POLYAMIDE-IMIDE COATING CONTAINING RESIDUAL SOLVENT; and polyurethanes as disclosed in U.S. Pat. No. 2,916,403, issued Dec. 8, 1959 to G. C. Calderwood, for BONDING COMPOSITIONS; as well as a wide variety of other bondable resins.
Polyesterimide resin insulated wire enamels are well-known and widely used in the art of forming magnet wire for high temperature and hermetic applications. Compositions and methods for forming polyesterimide insulated wire enamels are well-known, and the application thereof to wire to form magnet wire is conventional and well-known to those of ordinary skill in the art. See, for example, British Pat. No. 973,377, British Pat. No. 996,649, U.S. Pat. No. 3,426,098, and U.S. Pat. No. 4,145,334.
Polyester resin insulated wire enamels are also known and widely utilized. One particularly successful polyester magnet wire insulation resin is manufactured by the General Electric Company under the Trademark ALKANEX, and is disclosed in U.S. Pat. No. 2,936,296, issued May 10, 1960, to F. M. Precopio, et al., for POLYESTER FROM TEREPHTHALIC ACID, ETHYLENE GLYCOL, AND A HIGHER POLYFUNCTIONAL ALCOHOL.
Polyamide-imide resin insulated wire enamels are known and widely used in the art of producing magnet wire. See, for example, U.S. Pat. No. 3,428,486, issued Feb. 18, 1969, to N. J. George, for POLYAMIDE-IMIDE ELECTRICAL INSULATION; U.S. Pat. No. 3,475,212, issued Oct. 28, 1969, to H. J. Back, for METAL CONDUCTOR COATED WITH NONLINEAR COPOLYESTER BASECOAT LAYER AND POLYAMIDE-IMIDE OUTER LAYER; U.S. Pat. No. 3,528,852, issued Sept. 15, 1970, to E. H. Olson, et al., for DUAL-COATED ELECTRICAL CONDUCTOR; and U.S. Pat. No. 3,695,929, issued Oct. 3, 1972, to F. A. Sattler, for CONDUCTORS INSULATED WITH A POLYMERIC AMIDE-IMIDE-ESTER AND AN AROMATIC POLYIMIDE OR AROMATIC POLYAMIDE-IMIDE OVERCOAT. In the commercial preparation of magnet wire, insulation coatings are conventionally applied to strands of wire in a wire tower such as disclosed in U.S. Pat. No. 3,183,604, issued May 18, 1965, to J. D. Stauffer for APPARATUS AND PROCESS FOR REMOVING SOLVENTS FROM COATINGS ON METAL, or U.S. Pat. No. 3,183,605, issued May 18, 1965, to D. D. Argue, et al., for APPARATUS FOR COATING METALS. In the wire tower, the wire to be coated is passed through an enamel applicator and receives a coating of resin and solvent in liquid form. The wire then passes through a vertical oven or furnace in which the solvent is removed and the coating cured on the wire. Multiple passes can be provided to increase the coating thickness. As pointed out in the above wire tower patents, care must be taken in the application and cure of the enamel coating to prevent the formation of blisters and other imperfections in the enamel coating.
Certain known self-bonding varnishes or coatings for various members, such as laminae and magnet wires, have many desirable characteristics and properties; however, the self-fusing or bonding in certain cases is believed to require excessively high temperatures or an excessive amount of time, and many of the self-bonding overcoats are believed to be unable to withstand many of the common environmental tests including chemical resistance toward various refrigerants, such as fluorinated hydrocarbons. Furthermore, many such self-bonding overcoats are applied from solutions containing hazardous solvents, and it is desirable to apply such resins and/or varnishes from media and/or carriers which are non-hazardous, for example, from water-based compositions.